Photoionization as the secondary mechanism in a Townsend breakdown

An extrapolation of available data on photoionization is used to make calculations for determining the probability of releasing succeeding electrons at the cathode in a Townsend breakdown of a sparkgap. These calculations indicate that photoionization is a plausible secondary mechanism in a Townsend breakdown of gaps of the order of 1 cm (centimeter) at atmospheric pressure, and also that, when an over voltage is applied to a gap, photoionization is greatly increased and can account for very rapid breakdown.